A gas turbine generally includes an axial compressor, a combustion section downstream from the compressor and a turbine section downstream from the combustion section. The compressor generally includes a casing and an inlet that is disposed at an upstream end of the casing. The combustion section generally includes a plurality of combustors arranged in an annular array around an axially extending shaft that extends at least partially through the gas turbine. The turbine section generally includes an outer casing that at least partially circumferentially surrounds the shaft. The turbine section further includes multiple rows or stages of stationary vanes that extend radially inward from an inner surface of the outer casing so as to circumferentially surround the shaft. Each row of the stationary vanes is axially separated by a row of turbine blades that extend radially outward from the shaft.
In operation, a working fluid such as air is ingested through the inlet of the compressor and is progressively compressed as it flows through the compressor towards the combustion section. A primary portion of the compressed air is routed to each combustor of the combustion section for cooling various hot gas path components and/or for mixture with a fuel for combustion.
A secondary portion of the compressed air is extracted from the compressor upstream from the combustion section through one or more extraction ports that extend through the compressor casing. The secondary portion of the compressed air is routed from the compressor through one or more fluid conduits and/or couplings and into various cooling circuits defined within the turbine section of the gas turbine. The secondary portion of the compressed air is used as a cooling medium to cool various components of the turbine section such as one or more of the rows of the stationary vanes.
Generally, one or more flow control valves such as modulating valves are disposed between the extraction ports and the turbine section to control the flow rate of the secondary portion of the compressed air that flows from the compressor into the turbine section. During base-load or peak-load operation of the gas turbine, when the cooling requirements for the turbine section are the highest, the flow control valves are set to allow a higher flow rate of the compressed air than when the gas turbine is being operated at a part-load or in an unloaded condition. During part-load operation, when the cooling requirements of the turbine section are reduced, the flow control valves restrict or limit the flow of the compressed into the turbine section to improve compressor and/or overall gas turbine efficiency. One concern with this type of system for controlling the flow rate of the compressed air to the turbine section is that the flow control valves require measurement and feedback control, thereby potentially compromising the overall reliability of the gas turbine.
In alternate gas turbine configurations, the flow control valves do not modulate or actuate to reduce the flow rate. As a result, excess compressed air is routed into the turbine section during part-load operation, thereby reducing the overall efficiency of the compressor and/or the gas turbine. Accordingly, an improved system for reducing the flow rate of the compressed air flowing from the compressor to the turbine section during part-load operation of the gas turbine would be useful.